COL9A3 and multiple epiphyseal dysplasia: However, myopathy does not appear to be a consistent feature of MED caused by COL9A3 mutations [Paassilta et al., 1999; Nakashima et al., 2005] and it has been suggested that the degree of muscle weakness correlates with the severity of the MED phenotype [Nakashima et al., 2005].